Oscilloscope device



sept. 14, 1948.

T. H. WITHERBY ET AL OSCILLOSCOPE DEVICE Filed Nov. 27. 144

Patented Sept. 14, 1948 UNITED STATES PATENT OFFICE 2,449,524, os'oI'LLoscoPE -nnvlcn Thomas Hl Witherby, Buffalo, Y., and Harry E. Farnsworth, Providence, R.I., assignorsto the Unitedv States cfAmerica as representedby theSecretary of War f Application November 27, 1944', sensitive. 565,578

with respect to the second anode and the corre' spending adjusted values of the irst anode po` tential, VA1. These detects are interdependent. Thus, in order to keep the spot in best focus as its position on the screen is varied over the whole area, it is necessary to adjust both Vai and the mean potentials of the deecting plates. Also'a variation of the grid potential for a given spot position requires an additional adjust-ment of VAL It is, therefore, an object of this inventionv to provide a control circuit for automatically ad-v justing both the mean potentials M1',2 and M3',4,y andthe rst anode potential, Vin, as the applied deecting voltages are varied by a-mounts which correspond to deflections of the spot overl the whole area. of a screen.

The ciircuit is constructed on the assumption that the required correctionv potentials are proportional to the square of the deflection potentials. It is also assumed that the total correction to vbe applied to the first anode potential VAl is the algebraic sum of the individual cor` rections for the horizontal and vertical deilections. The correction applied to the mean po'- tential of each pair of delecting plates is'proportionlal to the square of the instantaneous deiiect-v ing potential, the rate being manually adjustedy by a potentiometer. The results which vhave been obtained experimentally show that these assumptions are justified in general, in other word's, the

circulit is constructed on the assumption that the required correction curves of incrementI M and increment Vm along the axis of deflection mayl be approximated by two parabolas, having a com" mon axis, vwhose curvatures may be varied inde' pendently. Correction'salong the two axes of deection may be made independently. It is also' assumed that the desired result can be obtained by varying ML2 as a function of the deflection potentials on D1D2 only, and similarlyforMsA and D3D4, and that the required adjustment of VAi at a point y) is given by the algebraic sum of the adjustments required for the two points (o, y) and (m, o). .The resultsy which 2 have been obtained show that theseassumptins are justied i-n general.'

This' and other objects ,are attained by the circuit andv arrangement of elements hereinafter described andsho'wri onthe accompanying draw# ings,' forming" a part" hereof, and in' which t'ltie` i'igur'is a schematic diagram ofv a circuit' embodying the invention; Referring to the circuit diagram, the system is symmetrical with respect to vvertical Fand leciti-[ Zontal' input terminals. Tubes l, 2, 3, 4L and'` 5' CQnSfdermg'. ,for

are of the twin triode type'. the present only the, vertical amplifier circuit, the iirstv twin tube I` Uis an inputfcathode `follower and amplliierlA Twin triodeZ is a genera-' 4 tor for producing square law focus correction Each triiode is biased just to cut off,

voltages. by adjustment pf cathode potentiometers rc and rj fed from -l-Bthroug'h resistor Tio. Since each component tube operates on the'curvedportion' of its characteristic curve, the plate signaloutput'` of each tube is proportional tothe square of its' input grid voltage, and thus providespthe type o f focus correction voltage required; These cor` rectivevoltages appear across plate potentiome-- ters rs and r9. Appropriate'portons of voltage drop appearing across r land 19v` are fed to the:

grids of the following tubes Sand 4 shown. The plates of bothtriodes ofA tube 2 are confnected together by lead l`l. Thus a positive signalk applied to the" grid of either tube gives a` negative signal at thecombined plates, Aa riega' tive'signal having no effectbecaus'e'oi the block"- i'ng' bia-s.

The thifdtwi-tllo'def affisajtwdstage amplifier: whose input is adjusted by potentiometer- 11g ofj tube 2. Its output: isappliedthrouglillead I2 t'o' the'accelerating grids of pentode tubes Sand; 1,

connected in parallel;- The control gridof peril tode 6 is excited bythe voltage'dropacrossplate resistor ra of-the second partoftube l, through'- lead l3,whilel control gnid of pentode 1 is'simi-e larly excited by the drop across cathode resistorV r2 through lead M Thus the'plate output voltages of tubes Sand l appearing across resistors r11 and nzare in phase opposition and are applied separately, to the vertica\l deiec'ting plate D3 and D4 of the' cathode ray tube', thereby mainltaining a balanced potential with respect to ground.

Since-1the'acceleratingfgrids Yof tubes vl5 and 'l are in parallel; the pairv ofA vertical de flectin'g plates D3 and D, are c arriel simultaneously above the mean" and nol signal potentiali in accordance with thev square'law potential derived Afunctions of tubes I', 2', and 3 are identical' with those of tubes I, 2, and 3. The adjusted output of square law correction generator 2 is fed through amplifier 3 through lead I2 to the accelerating grids (Lin parallel) of output pentodes 6 and 'I'. This varies the mean potential of horizontal deflection plates vD1 and Dz in 'accordance with the desired horizontal correction.

The adjusted output of rst element of square law correction generator 2 is fed from plate resistor ra through lead I5 to grid r174,1 of tubeA.vr Similarly thel adjusted 4output of correction generator 2' Lis fed from plate resistor r' through lead I5.' to grid gm. The plates of both elements of tube, 4 are corrected in parallel by lead I'I, hence the correction effects of both channels are added algebraically in plate resistor T13 from which the resultant effect is applied to control grid g5',1 ofl amplifier tube 5. The amplied correcti'on 'voltage is fed by leads 2D and 2I to they accelerating anode A1 of the cathode nay tube.

` The overall result of the corrective system is to apply a square law correction voltage to the accelerating a-node of the cathode ray tube which is the algebraic sum of the corrections for the separate channels and to provide square law correction voltages for the individual pairs of deecting plates thereby automatically maintainingQthe electron beam inv sharp focus at ali parts of the screen. 1

A Referring to the circuit diagram and considering only thevertical amplifier, the first tube I, is aninput cathode follower and a phase splitter. The second tube 2 is the correction signal detector. Tubes I, 2, 3 are of the 6SN7 type, twin triode, class A ampliners. Y In the second tube 2, the plates are tied togetheuand each triode of tube 2 is biased separately just to cut-off. There is thuswa negative signal at the plates for either a positive or a negative deflection signal. Since the tube is operating on the curved portion of the characteristic Asp is approximately proportional to (Aeg)2 which means the correction curve will be approximately a parabola.V ep is the plate voltage and ez the grid voltage.

The third tube 3, is a two stage amplifier which drives the screens of the output tubes with a correction signal 180 out of phase. The output pentod'es actas mixers for the deflection and correction signals, thus making a mean potential correction.

Thecircuit for horizontal deectio-n is identical.

Attenuated correction signlals are mixed in tube 4, which is of the variable mu class A amplier. The following tube 5, which is of the 6SN7 type, was found necessary in order there be suicient signal voltage at the rst anode AI. One stage of amplification would sufce, but then the phase would be inverted.

By means of theV above circuit arrangement the various voltages of a cathode ray tube are automatically adjusted to maintain the tube in focus.

The above description is to be considered as illustrative land not restrictive of the invention, of which modifications can be -made without departing from the scope and spirit of the invention as set forth in the appended claims.

'I'he' invention having been described, what is claimed is:

' 1. In a, circuit including signal input terminailsgaY cathode nay tube having deflecting plates, and Yafocusing electrode; means for generating a voltage-'substantially proportional to the square of'theI'signalinput voltage; and vacuum tube means for applying said square law voltage to said focusingr electrode for automatically cor- 2.fIn alcircuit having signal input terminals and including a cathode ray tube having deecting plates, anda focusing electrode; means for generating a Vvoltage substantially proportional to anexponential power of said signal input voltage; and vacuum tube means for applying a portion of vsaid exponential voltage as a correction tosaid focusing electrode for automaticaily correcting the focus.

3. YIn a circuit having signal input terminals and including a cathode ray tube having deflecting plates, anda focusing electrode; means for generating a non-linear voltage substantially proportion to an exponential power of the signal input Voltage; said means comprising an amplier biased-,substantially to cut off and excited from saidinputvoltage; and means for applying a portion of said exponential voltage to said focusing electrode for automatically correcting the focus.v Y

f1. Ima circuit having signal input terminals and including a cathode ray tube, having deecting plates and a rst anode; means for automatically correcting the focus during deflection, said means comprising a biased amplifier excited fromsaid signal input for generating an exponentiall focus correction voltage and vacuum tube means iorapplying said correction voltage to said rst anode.

5..In a .circuit hiaving signal input terminals and includinga cathode ray tube having deflecting placesand a focusing electrode, means for automatically correcting said focus as a function of said input voltage; said means comprising a, biased amplifier excited from said signal input for generating an exponential correction voltage andvacuum tube means for changing the mean potential of one pair of deflecting plates,` in accordance with said correction voltage.Y

6. In a circuit having two input channels and including a cathode ray tube having vertical and horizontal deflecting plates and a first anode; meansffor automatically correcting the focus as afunctionpof .the combined input voltages; said means comprising a biased amplifier for each channel and each excited by its channel input voltage, vacuum tube means for adding the sepiarate correction voltages and for applying the resultant voltage to said first anode.

.- 7.In :a circuit having two input channels and 4includingy a. cathode ray tube having vertical andrhorizontal deflection plates and a focusing electrode; -m'eans for automatically correcting the focusas a function of the deflection voltages of each channel; said means comprising la biased amplifier for each input channel biased substantially to cut oli, and vacuum tube means for Kchanging the mean potential of each pair of deflectling plates in accordance with the output of the corresponding biased amplifier.

8. In a cathode ray tube circuit including vertical and horizontal i-nput channels, a cathode ray tube having vertical and horizontal deflecting plates and a iirst and second anode; means for automatically `correcting the focus as a function of the input voltages of each channel; said means comprising an amplifier for eaich channel biased substantially to cut 01T for generating a correction voltage, vacuum tube means for changing the mean potential of each of said pairs ol? deflecting plates in accordance with the correction voltage of the corresponding channel, and means for adding said chiannel correction voltages and applying the resultant voltage to said first anode.

9. In a cathode ray tube circuit including vertical and horizontal input channels, a cathode ray tube having vertical and horizontal delecting plates and a rst and second anode; means for automatically correcting the focus as a function of the input voltages in each channel; said means comprising an amplier for each channel biased substantially to cut off for generating a correction voltage, means for manually adjusting the output of each' biased amplifier, means for changing the mean potential of each pair of deflecting plates in accordance with the correction voltage of the corresponding channel, and means for adding said channel correction voltages and applying the resultant voltage to said rst anode.

10. In a cathode ray tube circuit including vertical and horizontal input channels, a cathode ray tube having vertical and horizontal deecting plates, a focusing electrode and means for automatically correcting the focus during deflection, including a focus correction generator for each channel; means for adding algebraically said correction generator voltages and applying the resultant to said focusing electrode said adding means comprising a pair of amplifier tubes having a common output resistor each tube having a plate. cathode and grid; said plates being connected in parallel and each grid excited from the output of one of said correction generators.

1l.. In a cathode ray tube circuit including a cathode ray tube having vertical and horizontal pairs of defiecting plates, first and second input channels for said pairs of deflecting plates respectively; a focusing electrode and means for automatically correcting the focus, said correcting means including iirst and second focus correction generators for said channels respectively and means for changing the mean potential of each pair of deflecting plates in accordance with the output of the first and second correction generators respectively; each said potential changing means including a pair of ampliiier tubes; each tube being provided with at least two grids, a cathode and an anode, the anodes corresponding to the first channel being respectively connected to the vertical deflecting plates, the anodes corresponding to the second channel being respectivelyv connected to the horizontal deflecting plates, and the control grids of each pair of tubes being excited in phase opposition from the corresponding input channel respectively, said second grids in each pair of tubes being connected together, and excited by the corresponding focus correction generator.

12. In a cathode ray tube circuit including vertical and horizontal input channels, a cathode ray tube having vertical and horizontal deflecting plates, focusing electrodes and means for automatically correcting the focus during deiiection including a focus correction generator for each channel, means for changing the mean potentials of said deflecting plates in accordance with the respective outputs of said correction generators; said means comprising a pair of amplier tubes for each' channel, each tube being provided vvith two grids, each pair of control grids being excited in phase opposition from one channel input, said amplier tubes including anodes respectively connected to the corresponding deection plates and the second grids of each pair being connected together and respectively excited by their complementary focus correction generator.

13. In ya system for a cathode ray tube having means for horizontal and vertical deflection of an electron beam, and vertical and horizontal input channels each including a preamplifier; means for automatically correcting the focus of said beam comprising generator means in each deection channel adapted to produce focus correction voltages substantially proportional to an exponential power of the signal voltage; means for adding the separate channel correction voltages and applying the resultant to the first anode of said cathode ray tube; and potential changing means for changing the mean potential of each pair of deflecting plates in accordance with' the correction voltage for the corresponding channels; said generator rneans comprising two pairs of amplifier tubes biased substantially to cut ofi, the plates of each pair being connected in parallel and having an output impedance, and grids excited in phase opposition from their complementary preamplier; said adding means comprising a pair of amplifier tubes having plates connected together and having grids excited by th'e complementary correction generators; means for applying anode potential to the plates of said rst pair of amplifier tubes including resistance means in series with such plates; means for applying anode potential to the plates of said second pair of amplifier tubes including resistance means in series with such plates of the second pair; said potential changing means comprising a pair of amplifier tubes for each channel each having at least two grids, the control grids of each pair being excited in phase opposition by their complementary preamplilers and Whose plates are separately connected to the corresponding pair of delecting plates and Whose second grids are connected together and excited by the corresponding correction generator.

THOMAS H. WITHERBY. HARRY E. FARNSWORTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,089,430 Roys et al Aug. 10, 1937 2,107,392 Schlesinger Feb. 8, 1938 2,153,140 Diehl et al Apr. 4, 1939 2,315,848 Geohegan Apr. 6, 1945 2,318,197 Clark May 4, 1943 2,363,810 Schrader et al Nov. 28, 1944 2,368,449 Cook Jan. 30, 1945 2,399,754 Miller May 7, 1946 2,411,963 George Dec. 3, 1946 2,418,133 Miller et al Apr, 1, 1947 

